1. Field of the Invention
This invention relates to a device for minimizing far-end crosstalk between digital transmission lines and, more particularly, to such a device which is included in a half-duplex digital terminal or intermediate station which serves a section of a two-wire line whose other end is a grouping point of the digital transmission lines in a link.
2. Description of the Prior Art
The invention can be applied especially to a digital transmission link such as a transmission cable including a digital subscriber line, which operates in the half-duplex transmission mode. The range, i.e., effective transmission distance, of current subscriber lines is affected by crosstalk phenomena to a greater extent than constraints brought about by attenuation in the line which determines the ability of receiving means of the subscriber stations to detect and regenerate the signals received thereby. The range also affects the propagation times in the lines. One of the crosstalk components, namely near-end crosstalk, is reduced by the fact that one of the terminal stations, such as the local telephone exchange serving all the subscriber lines, synchronizes the transmissions of digit packets to the subscriber stations. The presence, however, of the other component, namely far-end crosstalk, is still felt and this produces a considerable disturbance which may be an error source when regenerating the signal in the receiving channel of the subscriber station.
Apparatus for minimizing the far-end crosstalk effect in a half-duplex digital line that is part of a cable is disclosed in the article by K. TANAKA et al., published in NTG FACHBERICHTE, Pages 86-90, Vol. 73, 1980, ISSLS 80 "The International Symposium on Subscriber Loops and Services", September 15-19, 1980, Munich, Federal Republic of Germany. This apparatus includes an equalizing amplifier in the transmitting channel of a line end station; the equalizing amplifier gain is controlled by an automatic gain control circuit of the equalizing amplifier in the receiving channel of the end station. The transmission and reception channels thus each comprises an equalizing amplifier.